We found that breast cancer cell lines positively associated with the tamoxifen sensitivity signature exhibited significantly higher expression levels of ESR1, the estrogen receptor and molecular target of tamoxifen, compared to lines showing negative pathway activation scores (p = 2.12×10−7, Accuracy 84.3%, Sensitivity 100%, Specificity 75%) (Figure 1B and Table S1). Here, ESR1 is linked to breast cancer.